Hall current plasma sources when used on satellites are known as Hall thrusters. Such thrusters are plasma-source-based propulsion devices that have found application onboard spacecraft for station keeping, orbit transfers, and interplanetary missions. A combination of thrust efficiency, thrust density, and specific impulse makes Hall plasma sources effective for such varied space missions. Hall current plasma sources typically operate between 40% and 70% efficiency, with a thrust density of 1 mN/cm2, and specific impulses of between 1000 s and 3000 s. Hall current plasma sources have been used for space missions since the 1970s, and American-designed Hall current plasma sources have been in use since 2006.
Hall current plasma sources generate thrust through the formation of an azimuthal electron current that interacts with an applied, quasi-radial magnetic field to produce an electromagnetic force. The plasma source operation results in ions being accelerated away from the source by an electric field that exists in the region of the applied, quasi-radial magnetic field. Used as a thruster, these sources provide an attractive combination of thrust and specific impulse for a variety of near-earth missions and, in many cases, they allow for significant reductions in propellant mass compared to conventional chemical propulsion. The range of thrust and specific impulse attainable by Hall current plasma sources makes them applicable to a variety of commercial and science missions. Many such missions, however, have only a limited amount of power and volume available. Similar constraints exist in plasma processing vacuum chambers where higher thin film deposition rates are desired, but are prevented due to the relatively low ion current provided by existing ion beam-based ion assist sources.
Small spacecraft (also known as Cubesats, nano-spacecraft, or microsatellites) are designed to fit within a very low mass budget and a constrained volume. To date, these small spacecraft vehicles have only been operated in Earth orbit, typically as “ride along” secondary payloads on other missions, but there is considerable interest in expanding the capability of these small spacecraft into lightweight, low cost missions performed throughout and beyond Low Earth Orbit. The lack of propulsion on Cubesats severely limits their capabilities and this means that the satellites have no useful control over their orbits once deployed. Limited power and surface area onboard these vehicles have resulted in primarily low specific impulse propulsion systems being considered, resulting in minimal orbit change capability and usability.
Although there are a number of small propulsion systems currently available, they only demonstrate a useful lifetime of less than approximately 1000 hours, which is insufficient if these devices are to be used as the primary propulsion system for deep space missions or long-term missions in near Earth orbits. In addition, these propulsion systems are typically heavy and can occupy a significant portion of the limited volume on these vehicles.